Convolvulus L. (incl. Calystegia R. Brown)
Convolvulus as currently circumscribed (i.e. including Calystegia) is a genus of ca. 275 more or less widely distributed species. Three species are native in Belgium (Lambinon & al. 2004): Convolvulus arvensis L., Convolvulus sepium L. (syn.: Calystegia sepium (L.) R. Brown) and C. soldanella L. (syn.: Calystegia soldanella (L.) R. Brown). Calystegia is morphologically well separated from Convolvulus and forms a monophyletic group. However, molecular data show that it is in fact nested in Convolvulus (Stefanovic & al. 2003). It should therefore be included in the latter or Convolvulus should be further divided in several additional genera. A monograph of the genus was recently published (Wood & al. 2015); for pragmatic reasons Calystegia was excluded from it.
Native Convolvulus arvensis is very variable, especially in pubescence and leaf shape. Non-native forms are sometimes seen in man-made habitats. Most typical (and perhaps meriting a more elevated taxonomic status; see Stace 1972) probably is the southern European var. linearifolius Choisy with linear to oblong-lanceolate leaves, often with very prominent backwardly directed auricles). Such plants were collected on a grain dump in the port of Roeselare in 1999 and are also sometimes seen in imported containers with olive trees in plant nurseries (Hoste & al. 2009).
Convolvulus sepium belongs to a taxonomically difficult species complex in which hybridisation and introgression frequently occur. Several species of this complex are cultivated in Europe (in addition to Convolvulus sepium at least four others of which Convolvulus dubius and Convolvulus silvaticus probably are the most widespread in cultivation; see Hyam 2000). R.K. Brummitt revised the Belgian collections of Convolvulus in 1960. He only recognised Convolvulus dubius from Belgium and it is represented by very few collections. Non-native taxa of Convolvulus are apparently very rarely cultivated in Belgium (or seldom escape), or are simply not collected due to confusion with native C. sepium (Verloove 2011). Introgression has further blurred the specific limits between these species and several hybrids have been described (Brummitt & Chater 2000). Finally, non-native forms of Convolvulus sepium might have been overlooked as well. The references beneath provide valuable information for the distinction of taxa within this species complex.
Convolvulus japonicus Thunb. (syn.: Calystegia japonica (Thunb.) Choisy) has been claimed from Belgium as well (Lambinon & al. 2004) but apparently without obvious source. Moreover, it is unclear which taxon is exactly meant. The correct name for the usual garden plant appears to be Convolvulus pubescens (Lindl.) Thell. (syn.: Calystegia pubescens Lindl.).
1. Bracteoles ovate, at least partly obscuring sepals. Stigmas swollen. Ovary unilocular === 2
1. Bracteoles lanceolate to filiform, not obscuring sepals. Stigmas filiform. Ovary two-celled === 5
2. Stem not twining (procumbent). Leaves reniform, thick. Corolla pink with 5 white stripes (native) === Convolvulus soldanella
2. Stem twining. Leaves triangular and sagittate, thin. Corolla white or pink with white stripes === 3
3. Bracteoles acute at apex, usually 10-18 mm wide when flattened, not or scarcely overlapping at edges, scarcely obscuring sepals, not saccate at base. Leaves shiny, leaf sinus V-shaped. Corolla length rarely exceeding 50 mm === C. sepium
3. Bracteoles more or less rounded to slightly emarginate at apex, usually 18-40 mm wide when flattened, strongly overlapping at edges and largely obscuring sepals, distinctly saccate at base. Leaves often dull, leaf sinus square or rounded, not V-shaped. Corolla length usually exceeding 50 mm === 4
4. Bracteoles usually 18-25 mm wide when flattened. Corolla pink, often with 5 white stripes, 50-75 mm. Peduncle (at least some) with a narrow, wavy wing. Peduncle, pedicels and lower side of young leaves (especially near sinus) sparsely shortly hairy. Sinus of leaves more or less square === 1. Convolvulus dubius
4. Bracteoles usually up to 40 mm wide when flattened. Corolla white (rarely pale pinkish with white stripes), 50-90 mm. Peduncle not winged. Plant glabrous. Sinus of leaves rounded === 2. C. silvaticus
5. Leaves gradually tapered to base, without distinct petiole, entire at base. Corolla pale bluish with white and yellow bands. Stem procumbent to ascending, not twining. Ovary and capsule hairy === 3. C. tricolor
5. Leaves very abruptly narrowed into distinct petiole, hastate to sagittate at base. Corolla white or pinkish. Stem twining. Ovary and capsules glabrous (native) === C. arvensis
Brummitt R.K. (1972) Calystegia. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 78-79.
Brummitt R.K. (1998) Calystegia. In: Rich T.C.G. & Jermy A.C. (eds.), Plant crib: 231-233. BSBI, London.
Brummitt R.K. & Chater A.O. (2000) Calystegia (Convolvulaceae) hybrids in West Wales. Watsonia 23: 161-165.
Hoste I., Verloove F., Nagels C., Andriessen L. & Lambinon J. (2009) De adventievenflora van in België ingevoerde mediterrane containerplanten. Dumortiera 97:1-16.
Hyam R.D. (2000) Calystegia. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 114-115.
Jauzein P. (1995) Flore des champs cultivés. INRA, Paris: 898 p.
Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.
Sa’ad F. (1967) The Convolvulus species of the Canary Isles, the Mediterranean Region, and the Near and Middle East. Bronder Offset, Rotterdam: 287 p.
Spaulding D.D. (2013) Key to the bindweeds (Calystegia/Convolvulus, Convolvulaceae) of Alabama and adjacent states. Phytoneuron 2013-83: 1-12. [available online at: http://www.phytoneuron.net/2013Phytoneuron/83PhytoN-Bindweeds.pdf]
Stace C.A. (1972) Convolvulus. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 79-82.
Stace C. (1997) New flora of the British Isles, 2nd ed.: XXVII + 1130 p. Cambridge University Press.
Stefanović S., Austin D.F. & Olmstead R.G. (2003) Classification of Convolvulaceae: a phylogenetic approach. Syst. Bot. 28: 791-806.
Sell P. & Murrell G. (2009) Flora of Great Britain and Ireland. Vol. 3 Mimosaceae – Lentibulariaceae. Cambridge University Press, Cambridge: XXVIII + 595 p.
Verloove F. (2011) Weinig gekende Calystegia-taxa in België. Dumortiera 100: 25-29. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_100/Dum%20100_25-29_Calystegia_Verl...
Wood J.R.I., Williams B.R.M., Mitchell T.C., Carine M.A., Harris D.J. & Scotland R.W. (2015) A foundation monograph of Convolvulus L. (Convolvulaceae). PhytoKeys 51: 1-278. [available online at: http://phytokeys.pensoft.net/articles.php?id=5459]